Method and apparatus for treating pre-enriched ammonia

ABSTRACT

The pre-enriched ammonia is delivered into the exchange column prior to the final enrichment stage and is placed into a material exchange with a portion of the deuterium-impoverished water from the rectifying column. The material exchange enriches the water with deuterium. The enriched water is then fed into an intermediate point in the rectifying column for final enrichment.

United States atem Hartmann et al.

[ Feb. 22, 1972 METHOD AND APPARATUS FOR TREATING PRE-ENRICHED AMMONIAInventors: Fortunat Hartmann, Zurich; Hans Rudolf Gisler, Winterthur,both of Switzerland Assignee: Sulzer Brothers, Ltd., Winterthur,Switzerland Filed: May 5, 1969 Appl. N0.: 821,862

Foreign Application Priority Data May 8, 1968 Switzerland ..687l/68 U.S.Cl. ..23/204 C, 23/283, 23/312 W,

62/ 17 Int. Cl. ..C01b 5/02, B0 1 j 1/00, F25 3/00 Field of Search..23/204 R, 210 l, 283, 204 C,

[56] References Cited UNITED STATES PATENTS 3,028,222 4/1962 Eriksson..23/2 I 0 1 3,206,365 8/1965 Guernsey ..23/204 FOREIGN PATENTS ORAPPLICATIONS 903,367 8/1962 Great Britain ..23/ 204 PrimaryExaminerOscar R. Vertiz Assistant Examiner-Hoke S. MillerAtt0rneyl(enyon & Kenyon Reilly Carr & Chapin [5 7] ABSTRACT Thepre-enriched ammonia is delivered into the exchange column prior to thefinal enrichment stage and is placed into a material exchange with aportion of the deuterium-impoverished water from the rectifying column.The material exchange enriches the water with deuterium. The enrichedwater is then fed into an intermediate point in the rectifying columnfor final enrichment.

12 Claims, 1 Drawing Figure PATENTEDFEBZZ I972 3,644,093

Inventors,-

FOFPTUNAT HAQTMANN HANG FvZ/DOLF 615L157? METHOD AND APPARATUS FORTREATING PRE- ENRICHED AMMONIA This invention relates to a method andapparatus for treating preenriched ammonia. More particularly, thisinvention relates to a method and apparatus for treating a preenrichedammonia to process heavy water for a final enrichment stage.

l-leretofore, it has been known in the production of heavy water, topreenrich ammonia and to use this ammonia in a final enrichment processto produce heavy water. The preenrichment of the ammonia can takevarious forms. For example, the preenrichment can be carried out in adithermal" or monothermal"process.

in a monothermal preenrichment process, for example, a catalyticallyaccelerated isotope exchange between ammonia and synthesis gas and acountercurrent of liquid ammonia containing a catalyst produces anammonia enriched with deuterium; synthesis gas being converted intoliquid ammonia at the place where there is a low deuteriumconcentration, and ammonia being converted into synthesis gas at theplace where there is a high deuterium concentration. In a finalenrichment process, after the catalyst has been removed from thepreenriched ammonia and has been recycled into the preenrichment processat the places where there is a low concentration of deuterium, theammonia containing a high concentration of deuterium from thepreenrichment process receives further treatment and is finally used toproduce heavy water.

In a conventional final enrichment stage associated with a monothermalpreenrichment stage, for example, liquid ammonia is purified from thecatalyst, e.g., potassium amide (Kl-IN and taken from the preenrichmentstage at a place where there is a high concentration of deuterium, andis enriched in a rectifying column until it contains the requiredpercentage of deuterium. In the process, liquid ammonia is fed in, and acountercurrent of ammonium vapor, further enriched with deuterium, isfed into the common base. The low deuterium ammonia leaving the columnhead is condensed and recycled into the preenrichment stage. The ammoniacollecting in the bottom of the column and containing the requireddeuterium content, e.g., 99.8 percent, then has to be decomposed in acracking plant into its constituent elements, viz. nitrogen, deuterium,and small quantities of hydrogen-deuterium and hydrogen. The mixture isthen burnt with oxygen in a combustion chamber to form wet aircontaining a large proportion of heavy water vapor. Finally, the heavywater is condensed from the mixture in a condenser.

While only the most essential parts of the plant have been mentionedabove, it is noted that additional equipment such as adsorptionapparatus is generally also required in practice.

The conventional plant, which may often be associated with a differenttype of preenrichment stage, is very expensive and has the followingserious disadvantages. Owing to the low boiling point of ammonia at apressure of one atmosphere, considerable cooling is necessary in orderto rectify the ammonia since it is desireable for economic reasons thatthe column should not operate at an unduly high pressure. If the ammoniais rectified at higher temperatures, e.g. at the temperature of theenvironment, the column will need to be constructed as a pressurecontainer, and will be expensive and difficult to keep in a sealtightcondition.

Further, if the required final enrichment in deuterium took place in thepreenrichment stage, it would be necessary to circulate large quantitiesof synthesis gas and/or liquid ammonia having a high deuterium contentin the preenrichment stage at high temperatures. Consequently, even ifonly small leaks would occur in the preenrichment apparatus such mightallow large quantities of deuterium to escape.

Accordingly, it is an object of the invention to avoid relatively largedeuterium losses.

It is another object of the invention to obtain heavy water in aconsiderably more economic manner than heretofore.

Briefly, the invention provides a method and apparatus for treatingpreenriched ammonia with a countercurrent of water containing a lowdeuterium content so as to enrich the water with deuterium prior to afinal enrichment of the water to heavy water.

The apparatus includes a plant having an apparatus for evaporating atleast a partial current of the preenriched ammonia, at least oneexchange column into which the preenriched ammonia vapor is conveyed,and a rectifying column from which part of the liquified head product isconveyed into the exchange column. The exchange column functions so thatan isotope exchange occurs between the preenriched ammonia vapor and thewater and so that the water becomes enriched with deuterium and at leastmost of it is supplied through a means such as a pipe line into therectifying column.

The apparatus for initially evaporating the ammonia has a preenrichedstage comprising two exchange towers, an ammonia synthesis plant, anammonia cracking plant, and an evaporator for concentrating thecatalyst. This stage is advantageously constructed'so that a means suchas a pipe line for removing the preenriched ammonia vapor is connectedto the evaporator and leads to a condenser connected by at least onemeans such as a pipe line to a place in the preenrichment stage wherethere is a high deuterium concentration. In addition, a means such as apipe line branches off from a point between the line between theevaporator and the condenser and leads to the exchange column. Theammonia leaving the top of the exchange column is liquefied by acondenser from which at least some of the ammonia is conveyed back tothe preenrichment stage. Also, a means such as a pipe line leads fromthe head of the rectifying column in order to supply water having a lowdeuterium content into the exchange column, and a similar line leadsfrom the bottom of the exchange column so as to supply deuteriumenriched water to the rectifying column.

The water vapor impurities which may occur in the apparatus areeliminated from the ammonia which is recycled after condensation fromthe exchange column to the preenrichment stage, and dissolved ammoniaimpurities are eliminated from the enriched water taken from theexchange column, by using condensed ammonia to wash out the water vaporcontent in the ammonia before condensation and by removing the ammoniacontent from the water flowing downwards through the exchange columnbefore flowing into the rectifying column.

These and other objects and advantages of the invention will become moreapparent from the following detailed description and appended claimstaken in conjunction with the accompanying drawing in which:

The drawing schematically illustrates a plant utilizing the method andapparatus according to the invention.

Referring to the drawing, the heavy water plant includes a preenrichmentstage, an exchange stage and a final enrichment stage.

The preenrichment stage includes two exchange towers l, 2 in which amonothermal isotope exchange can take place, a cracking plant 3 in whichammonia is converted into a gaseous mixture of three molecules ofhydrogen to 1 molecule of nitrogen so as to supply the gas reflux(schematically indicated by a chain line) in the exchange towers 1, 2,and an ammonia synthesis plant 4 which supplies the liquid reflux(schematically indicated by solid lines) to the exchange towers l, 2. Inaddition, the preenrichment stage includes a means such as a pipe line 5through which the stage is supplied with, for example, 1N synthesis gas(N denoting the natural deuterium concentration) for ammonia synthesis.Thesynthesis plant 4 is also connected with a means such as a pipe line6 for conveying deuterium-impoverished ammonia from the plant 4.

The lower exchange tower 2 is connected via a means such as a pipe line7 to an evaporator 8 so that the liquid ammonia in which a catalyst asis known is dissolved can be concentrated. The evaporator 8 in turn isconnected via a means such as a pipe line 9 which completes the catalystcircuit to return the liquid ammonia to the feed line above or upstreamof the upper exchange tower 1. The evaporator 8 is also connected via ameans such as a pipe line 10 to a condenser 11 so as to direct theevaporated ammonia as a vapor to the condenser 11. The condenser 11 inturn isconnected via a means such as a pipe line 12 to thecracking-plant 3.

In use, liquid ammonia in the exchange tower l is enriched by isotopeexchange with the hydrogen from the synthesis gas until its deuteriumcontent is, e.g., 4 N, and is further enriched in the lower exchangetower 2 until its deuterium content is, e.g., 400 N. The liquid ammonia,in which the catalyst, e.g., potassium amide is dissolved, then flowsthrough the line 7 to the evaporator 8 and concentrated. Thenonevaporated ammonia containing the catalyst then flows back through aline 9 into the liquid ammonia feedline above the exchange tower 1.

The preenriched ammonia which has evaporated and separated from thecatalyst is removed from the evaporator 8 through the line 10. Most ofthe ammonia vapor is then liquefied in the condenser 11 and fed throughthe line 12 to the cracking plant 3, so that the ammonia can bedecomposed into its constituent elements nitrogen, hydrogen,hydrogendeuterium and deuterium.

The exchange stage is connected to the preenrichment stage by a meanssuch as a branch pipe line 13 which connects to the line between theevaporator 8 and condenser 11 so as to draw off a portion of thepreenriched ammonia vapor. The exchange stage includes an exchangecolumn 14 to which the branch line 13 connects at an intermediate point.This exchange column 14 can contain a perforated bottom, bubble trays,or packing material as is known. Also, the exchange stage includes acondenser 18 at the upper end which receives the vapor from the exchangecolumn to return the condensed vapor via a line 19 back to the crackingplant 3. An evaporator 20 is connected to the lower end of the exchangecolumn 14 and is connected to the final enrichment stage via a meanssuch as a pipe line 21 so as to convey the unevaporated liquid thereto.

The final enrichment stage contains a rectifying column which receivesthe line 21 at an intermediate point. In addition, a condenser 16 isconnected to the upper end of the rectifying column to deliver waterinto the rectifying column and via a means such as a pipe line 17 to anintermediate point in the exchange column 14 to deliver water thereinto.An evaporator 22 is connected at the lower end of the rectifying column15 and has a means such as a pipe line 23 for removing a highlyconcentrated heavy water therefrom.

During use, a small proportion, e.g., 4 to 5 percent, of the ammoniavapor taken from the evaporator 8 in the preenrichment stage is conveyedvia branch line 13 into the exchange column 14. In addition, a part ofthe vapor from the rectifying column head which is liquefied in thecondenser 16 used to cool the column 15 is fed via line 17 which isdisposed above line 13, into the exchange column 14. Thedeuteriumimpoverished water (head product) having a deuterium contentof, e.g., 300 N, thus flows down the exchange column 14 while thepreenriched ammonia vapor flows upwardly so that an isotope exchangeoccurs. As a result, the deuterium in the ammonia passes into the water.

After being collected in the evaporator 20, the deuterium enriched wateris fed via line 21 into the rectifying column 15 which as above can havea perforated bottom, a bubble tray or packing material while theremainder of the head product from the condenser 16 is delivered at thetop of the column 15 and the vapor from the evaporator 22 is deliveredat the bottom. The enriched water is then finally enriched by theisotope exchange which takes place in the rectifying column.

The finally enriched water then collects in the evaporator 22 which isused to heat the rectifying column 15 and is removed via the line 23.

It is noted that in the part of the exchange column 14 above the waterinlet line 17, the water vapor in the upward flow of ammonia vapor isalmost completely washed out in a number of separating stages, asfollows: ammonia is liquefied in condenser 18 and a portion is recycledas a reflux into column 14, so that the water vapor in the upward streamof ammonia vapor is absorbed by the downward stream ofliquid ammonia.Also, most of the condensed ammonia flows through lines 19 and 21 backto the cracking apparatus 3 in the preenrichment stage. in principle,however, the condensed ammonia can by recycled through line 19 toanother part of the preenrichment phase.

Further, in the part of column 14, below the ammonia vapor inlet line13, the dissolved ammonia content is removed by rectification in anumber of separating stages from the downward stream of deuteriumenriched water. To this end, a small amount of bottoms comprisingenriched water is evaporated in the evaporator 20 and recycled into theexchange column 14. As a result, the ammonia dissolved in the liquidphase continuously evaporates and passes into the stream upon rising.

While the exchange column 14 is shown as having three parts, an upperpart in which most of the water vapor is washed out of the upward streamof deuterium-impoverished ammonia vapor, a middle part in which thedeuterium in the ammonia supply is conveyed by isotope exchange into acountercurrent of water, and a bottom part in which most of thedissolved ammonia is removed by rectification from the downward streamof enriched water, the exchange column 14 can alternatively be replacedby three separate columns, each of which fulfills one of theaforementioned functions.

It is further noted that a heating or cooling medium, e.g., water, canbe supplied to the plant from outside. Further, the final product, i.e.,heavy water, taken from the rectifying column 15 through line 23 can bereplaced by adding an equivalent quantity of water through a feed line(not shown) terminating in line 17 or line 21. Ordinary water can beused for the replacement water.

The invention enables the heavy water, should the amount of concentratedwater produced in the rectifying column be insufficient, e.g., becauseof faults in the plant or during the starting up period and which wouldotherwise be useless, to be returned into the plant from a tapping pointin line 23 through a pipe line 24 connected into line 17 or a pipe line25 connected into line 21.

Further, the invention allows the rectifying column and, if necessary,the exchange column to have correspondingly larger diameters. Also, theinlet lines 24 and/or 25 can be con nected to a point for removingdeuterium-impoverished water in a reactor. As a result, the finalenrichment stage according to the invention, besides producing as muchheavy water as required, can also process heavy water whose deuteriumcontent has been reduced in a reactor.

What is claimed is:

l. A plant for producing heavy water from a material exchange betweenwater and ammonia comprising means for preenriching ammonia vapor withdeuterium,

at least one exchange column having means for receiving a portion of thepreenriched ammonia vapor at an intermediate point thereof,

a rectifying column having means for delivering a liquefied head productthereto for isotope exchange with a deuterium enriched vapor to produceheavy water,

means between said delivering means and said exchange column for feedinga part of the liquefied head product to said exchange column for isotopeexchange with the preenriched ammonia vapor therein,

means between said exchange column and an intermediate point of saidrectifying column for feeding deuterium enriched water from saidexchange column to said rectifying column, and

means for removing heavy water from said rectifying column.

2. A plant as set forth in claim 1 wherein said means for preenrichingammonia includes at least two exchange towers, an ammonia synthesisplant for supplying liquid reflux to said towers, an ammonia crackingplant for supplying gas reflux to said towers, an evaporator connectedto said towers for concentrating the preenriched ammonia vapor therein,and a condenser connected between said evaporator and said crackingplant for condensing a portion of the preenriched ammonia vapor thereinfor delivery to said cracking plant.

3. A plant as set forth in claim 2 further comprising a means betweensaid evaporator and said exchange column for conveying a portion of thepreenriched ammonia vapor to said exchange column, a condenser at thetop of said exchange column for liquefying ammonia vapor therein, and ameans connecting said condenser to said cracking plant for recycling theammonia thereto.

4. A plant as set forth in claim 1 further comprising a water supplypipeline terminating in said means for feeding the liquid head to saidexchange column.

5. A plant as set forth in claim 4 wherein said water supply pipeline isconnected to said means for removing heavy water whereby insufficientlyconcentrated heavy water can be recirculated through said supply line.

6. A plant as set forth in claim 4 wherein said water supply pipeline isconnected to a reactor outside said plant whereby deuterium-impoverishedheavy water from a reactor can be suppled to said plant.

7. A plant as set forth in claim 1 which further comprises a watersupply pipe line terminating in said means between said columns forsupplying water to said rectifying column.

8. A plant as set forth in claim 7 wherein said water supply pipe lineis connected to said means for removing heavy water wherebyinsufiiciently concentrated heavy water can be recirculated through saidsupply pipeline.

9. A plant as set forth in claim 7 wherein said water supply pipeline isconnected to a reactor outside said plant whereby deuterium-impoverishedheavy water from a reactor can be supplied to said plant.

10. A method of producing heavy water which comprises the steps ofpreenriching ammonia vapor with deuterium;

directing at least a part of the preenriched ammonia vapor into acountercurrent flow to water having a low deuterium content for isotopeexchange to enrich the water to a higher deuterium content; and

directing the enriched water with a liquefied flow of a head productcontaining water with a low deuterium content in a countercurrent flowto a vapor of the head product and enriched water for producing a finaldeuterium enriched heavy water.

11. A method as set forth in claim 10 which further comprises the stepof directing a part of the head product into the countercurrent flowbetween the preenriched ammonia and water having a low deuterium contentin counter flow to the preenriched ammonia.

12. A method as set forth in claim 10 which further comprises the stepsof washing out the water vapor in the uncondensed ammonia vapor flow atan upper end of said flow with condensed ammonia, and rectifying theammonia from the enriched water flow prior to directing the enrichedwater flow into the countercurrent flow with the vapor of the headproduct.

2. A plant as set forth in claim 1 wherein said means for preenrichingammonia includes at least two exchange towers, an ammonia synthesisplant for supplying liquid reflux to said towers, an ammonia crackingplant for supplying gas reflux to said towers, an evaporator connectedto said towers for concentrating the preenriched ammonia vapor therein,and a condenser connected between said evaporator and said crackingplant for condensing a portion of the preenriched ammonia vapor thereinfor delivery to said cracking plant.
 3. A plant as set forth in claim 2further comprising a means between said evaporator and said exchangecolumn for conveying a portion of the preenriched ammonia vapor to saidexchange column, a condenser at the top of said exchange column forliquefying ammonia vapor therein, and a means connecting said condenserto said cracking plant for recycling the ammonia thereto.
 4. A plant asset forth in claim 1 further comprising a water supply pipelineterminating in said means for feeding the liquid head to said exchangecolumn.
 5. A plant as set forth in claim 4 wherein said water supplypipeline is connected to said means for removing heavy water wherebyinsufficiently concentrated heavy water can be recirculated through saidsupply line.
 6. A plant as set forth in claim 4 wherein said watersupply pipeline is connected to a reactor outside said plant wherebydeuterium-impoverished heavy water from a reactor can be suppled to saidplant.
 7. A plant as set forth in claim 1 which further comprises awater supply pipe line terminating in said means between said columnsfor supplying water to said rectifying column.
 8. A plant as set forthin claim 7 wherein said water supply pipe line is connected to saidmeans for removing heavy water whereby insufficiently concentrated heavywater can be recirculated through said supply pipeline.
 9. A plant asset forth in claim 7 wherein said water supply pipeline is connected toa reactor outside said plant whereby deuterium-impoverished heavy waterfrom a reactor can be supplied to said plant.
 10. A method of producingheavy water which comprises the steps of preenriching ammonia vapor withdeuterium; directing at least a part of the preenriched ammonia vaporinto a countercurrent flow to water having a low deuterium content forisotope exchange to enrich the water to a higher deuterium content; anddirecting the enriched water with a liquefied flow of a head productcontaining water with a low deuterium content in a countercurrent flowto a vapor of the head product and enriched water for producing a finaldeuterium enriched heavy water.
 11. A method as set forth in claim 10which further comprises the step of directing a part of the head productinto the countercurrent flow between the preenriched ammonia and waterhaving a low deuterium content in counter flow to the preenrichedammonia.
 12. A method as set forth in claim 10 which further comprisesthe steps of washing out the water vapor in the uncondensed ammoniavapor flow at an upper end of said flow with condensed ammonia, andrectifying the ammonia from the enriched water flow prior to directingthe enriched water flow into the countercurrent flow with the vapor ofthe head product.